(1) Field of the Invention
The present invention relates to a system and method for displaying a present position of a moving object applicable to a navigation system for a vehicle.
(2) Background of the Art
A Japanese Patent Application First Publication (non-examined) Showa 58-223016 published on Dec. 24, 1983 exemplifies a previously proposed system for displaying a present position of a moving object such as a vehicle on a road map image.
In the previously proposed system, a running distance of the vehicle is detected by a running distance detector, a travel direction is detected by a direction detector, a displayed map is sequentially updated as the present position is moved such that a displayed point indicating the present position of the vehicle is passed through the displayed map, and the displayed point is synthesized (superposed) so as to display on the updated map.
In more details, the present position (X.sub.t, Y.sub.t) of the moving object at a certain time t in a plane of X-Y coordinates is derived from the following equation. EQU X.sub.t =X.sub.t-1 +.DELTA.l cos .theta..sub.t EQU Y.sub.t =Y.sub.t-1 +.DELTA.l sin .theta..sub.t
In the above two equations, (X.sub.t-1, Y.sub.t-1) denotes a previous position of the vehicle before .DELTA.T second, .DELTA.l denotes a running distance for a time .DELTA.t, and .theta..sub.t denotes a running direction for the time .DELTA.t.
However, since the previously proposed system calculates the present position by accumulating the running distances per unit time in the X-axis direction and in the Y-axis direction, respectively, detection errors of the running distance detector and direction detector are also accumulated. Thus, as the vehicle runs for a long period of time, large positional errors for the present position of the present position will eventually occur.